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Fair Value Measurements (Fair Value, Option, Quantitative Disclosures) (Detail) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 30, 2018 USD ($) $ / MMBTU $ / MWh | Dec. 31, 2017 USD ($)
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 297 |  | $ 307
Fair Value of Derivative Liabilities |  | 145 |  | 284
Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 170 | [1] | 166
Fair Value of Derivative Liabilities |  | 8 |  | 66
Fair Value, Measurements, Recurring |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Total assets | [2] | 5,650 |  | 5,379
Total liabilities |  | 145 |  | 284
Fair Value, Measurements, Recurring | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Total assets |  | 2,593 |  | 2,466
Total liabilities |  | 8 |  | 66
Fair Value, Measurements, Recurring | Commodity |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 148 |  | 258
Fair Value of Derivative Liabilities |  | 100 |  | 197
Fair Value, Measurements, Recurring | Commodity | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 105 |  | 166
Fair Value of Derivative Liabilities |  | 8 |  | 9
Fair Value, Measurements, Recurring | Level 3 |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Total assets | [2] | 98 |  | 157
Total liabilities |  | 6 |  | 7
Fair Value, Measurements, Recurring | Level 3 | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Total assets |  | 91 |  | 152
Total liabilities |  | 5 |  | 5
Fair Value, Measurements, Recurring | Level 3 | Commodity |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 98 |  | 157
Fair Value of Derivative Liabilities |  | 6 |  | 7
Fair Value, Measurements, Recurring | Level 3 | Commodity | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 91 |  | 152
Fair Value of Derivative Liabilities |  | 5 |  | $ 5
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 12 |  |
Fair Value of Derivative Liabilities |  | 6 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | 12 |  |
Fair Value of Derivative Liabilities |  | $ 5 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Minimum | Liabilities |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | (1) |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Minimum | Liabilities | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | (1) |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Minimum | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | (1) |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Minimum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | (1) |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Maximum | Liabilities |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | 6 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Maximum | Liabilities | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | 6 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Maximum | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | 7 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Maximum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | 7 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Weighted Average | Liabilities |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3],[4] | 0 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Weighted Average | Liabilities | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3],[4] | 0 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Weighted Average | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3],[4] | 1 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Level 3 | FTRs [Member] | Commodity | Weighted Average | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3],[4] | 1 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Commodity |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets | [5] | $ 65 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Commodity | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets | [5] | $ 58 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Commodity | Minimum | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3] | (2) |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Commodity | Minimum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3] | (2) |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Commodity | Maximum | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3] | 7 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Commodity | Maximum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3] | 7 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Commodity | Weighted Average | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3],[4] | 0 |  |
Discounted Cash Flow [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Commodity | Weighted Average | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3],[4] | (1) |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Physical Options [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 19 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 19 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Minimum | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | 27 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Minimum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | 27 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Minimum | Assets | Price Volatility [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [6] | 4.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Minimum | Assets | Price Volatility [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [6] | 4.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Maximum | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | 57 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Maximum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3] | 57 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Maximum | Assets | Price Volatility [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [6] | 61.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Maximum | Assets | Price Volatility [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [6] | 61.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Weighted Average | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3],[4] | 42 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Weighted Average | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MWh | [3],[4] | 42 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Weighted Average | Assets | Price Volatility [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [4],[6] | 37.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Level 3 | Electricity | Electricity | Weighted Average | Assets | Price Volatility [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [4],[6] | 37.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 2 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Fair Value of Derivative Assets |  | $ 2 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Minimum | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3] | 1 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Minimum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3] | 1 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Minimum | Assets | Price Volatility [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [6] | 13.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Minimum | Assets | Price Volatility [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [6] | 13.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Maximum | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3] | 7 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Maximum | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3] | 7 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Maximum | Assets | Price Volatility [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [6] | 44.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Maximum | Assets | Price Volatility [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [6] | 44.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Weighted Average | Assets | Market Price [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3],[4] | 3 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Weighted Average | Assets | Market Price [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Market price (per Dth, per MWh, per Gal) | $ / MMBTU | [3],[4] | 3 |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Weighted Average | Assets | Price Volatility [Member] |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [4],[6] | 23.00% |  |
Option Model [Member] | Fair Value, Measurements, Recurring | Natural Gas | Level 3 | Physical Options [Member] | Weighted Average | Assets | Price Volatility [Member] | Virginia Electric and Power Company |  |  |  |
Fair Value, Option, Quantitative Disclosures [Line Items] |  |  |  |
Price volatility (percentage) | [4],[6] | 23.00% |  |
[1] | Noncurrent derivative assets are presented in other deferred charges and other assets in Virginia Power’s Consolidated Balance Sheets.
[2] | Includes investments held in the nuclear decommissioning and rabbi trusts. Excludes $217 million and $88 million of assets at September 30, 2018 and December 31, 2017, respectively, measured at fair value using NAV (or its equivalent) as a practical expedient which are not required to be categorized in the fair value hierarchy.
[3] | Represents market prices beyond defined terms for Levels 1 and 2.
[4] | Averages weighted by volume.
[5] | Includes basis.
[6] | Represents volatilities unrepresented in published markets.

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